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Human Physiology > Cell membranes and signalling > Flashcards

Cell membranes and signalling Flashcards

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1
Q

functions of membranes

A

A selective barrier to the passage
of molecules
Detecting chemical signals from
other cells
Anchoring cells to adjacent cells
and to the extracellular matrix of
connective-tissue proteins

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2
Q

lipid rafts

A

Cholesterol, phospholipids, and specific proteins work together to curve the membrane and pinch off a section to form a vesicle.
This occurs through membrane bending, which is driven by proteins like clathrin, caveolin, or other coat proteins.
Cholesterol-rich lipid rafts help to stabilize this curvature due to their ordered nature.

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3
Q

types of junctions that can join cells

A

desmosomes
tight junctions
gap junctions

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4
Q

integrins

A

transmembrane proteins in plasma membrane that bind to specific proteins in extracellular matrix and link them to membrane proteins on adjacent cells

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5
Q

interstitial fluid

A

fills gaps between cells

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6
Q

desmosomes

A

Characterised by accumulations of
protein known as dense plaques
along the cytoplasmic surface of the plasma membrane.
These proteins serve as anchoring points
for cadherins.
function is to hold adjacent cells firmly
together in areas that are subject to
considerable stretching, such as the skin

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7
Q

cadherins

A

proteins that extend from the cell into the extracellular space, where they link up and bind with cadherins from an adjacent cell.

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8
Q

tight junctions

A

Form when the extracellular surfaces of
two adjacent plasma membranes join
together so that no extracellular space
remains between them
Tight junctions block the extracellular space so molecules can’t flow freely in the interstitial fluid

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9
Q

gap junctions

A

consist of protein channels linking the cytosols of adjacent cells.
connexins from the 2 membranes join to form protein-lined channels
only allows small molecules through

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10
Q

at any concentration difference, what does the magnitude of flux depend on?

A

temperature
mass of molecule
surface area
medium through which the molecules are moving

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11
Q

how is specificity of a protein channel determined

A

pore size
charge
binding sites

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12
Q

types of gated channels

A

ligand gated
voltage gated
mechanically gated

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13
Q

ligated gated ion channels (chemical messengers)

A

a specific molecule binds to the channel causing an allosteric or covalent change in the shape of the protein

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14
Q

voltage gated ion channels

A

changes in the membrane potential cause a movement of charged areas of the protein, altering its shape

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15
Q

mechanically gated ion channels

A

physically deforming (stretching) the protein changes its conformation

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16
Q

factors determining magnitude of solute flux through a mediated system

A

saturation of transport binding sites (influenced by solute concentration and affinity of the transporter to the solute)
number of transporters in the membrane
rate at which conformation change occurs

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17
Q

primary active transport

A

direct use of ATP which is hydrolysed by an ATPase protein transporter
transporter is phosphorylated
covalent modulation, causes conformational change that increases affinity of solute binding site

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18
Q

secondary active transport

A

use of an electrochemical gradient across a membrane against their concentration gradient

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19
Q

direction and magnitude of ion flux is dependent on

A

concentration and electrical difference
(electrochemical gradient)

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20
Q

sodium/potassium pump mechanism

A

ATP is associated to the transporter
binds 3Na+
binding sites for K+ are of low affinity
ATPase removes a phosphate and phosphorylates the transporter
conformational change reduces affinity for Na+ and exposes to extracellular fluid
new conformation increases K+ affinity and binding causes dephosphorylation, conformation reverts back to original so that K+ released in intracellular fluid

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21
Q

major primary active transport proteins found in most cells

A

Ca2+ ATPase
Na+/K+ ATPase
H+ ATPase
H+/K+ ATPase

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22
Q

secondary active transport mechanism

A

low Na+ inside cell, high solute
electrochemical gradient directs Na+ into cell
Na+ binds to one site, solute to another
both released into cell

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23
Q

osmosis

A

net diffusion of water across a
membrane, which is dependent on water
concentration

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24
Q

osmotic pressure

A

”force” required to prevent the flow of water into a solution

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25
osmolarity (total solute concentration) of extracellular fluid
285-300 mOsm
26
ligand
molecule/ion bound to a protein by either electrical attractions between oppositely charged ionic or polarised groups on the ligand and the protein or weaker attractions due to hydrophobic forces between nonpolar regions on the two molecules binding does not involve covalent bonds reversible
27
saturation
fraction of total binding sites that are occupied at any given time An equilibrium is rapidly reached between unbound ligands in solution and their corresponding protein-binding sites.
28
what 2 factors does % saturation of a binding site depend on
concentration of unbound ligand in solution affinity of the binding site for the ligand
29
two mechanisms in cells that selectively alter protein shape and alter enzymes affinity for substrates
allosteric modulation covalent modulation doesnt increase maximum rate
30
allosteric modulation
occurs when a protein has two binding sites of a protein to one of the sites alters the shape of the other one binding site is the functional site, the other is the regulatory site to which a modulator (ligand) binds
31
cooperativity
when a ligand binds to the first of several functional sites on a molecule, this induces a change that increases the affinity of other functional sites
32
covalent modulation
covalent bonding of charged chemical groups to some of the protein’s side chains. eg phosphorylation by kinases (dephosphorylation by phosphatase)
33
catabolism
breakdown of organic molecules
34
anabolism
synthesis of organic molecules
35
calorie
amount of heat required to raise the temperature of 1g of water 1°C
36
law of mass action
the concentration of reactants or products can determine the direction at which the net reaction proceeds
37
cofactors
magnesium, iron, zinc, copper Binding of a metal to an enzyme alters conformation the substrate– allosteric regulation
38
coenzyme
organic molecule It directly participates as one of the substrates in the reaction usually derived from vitamins
39
how to change concentration of enzyme
increase protein synthesis increase protein degradation
40
metabolic pathway
sequence of enzyme-mediated reactions leading to the formation of a particular product
41
rate limiting enzymes
often the sites of allosteric or covalent regulation Control of enzymes through allosteric or covalent modulation can be important in determining the direction of reversible/irreversible reactions
42
neurotransmitters
function rapidly over short distances
43
hormones
function slower, usually over longer distances
44
antagonists
drugs that acts as competitors to receptor dont cause response in cell
45
agonists
drugs that mimic the messenger trigger response in cell
46
down regulation
a decrease in the total number of target cell receptors for a given messenger
47
increased sensitivity
increased responsiveness of a target cell to a given messenger can be caused by upregulation
48
binding causes change in conformation of receptor, resulting in a change to...
permeability, transport properties or electrical state of the cell metabolism secretory activity rate of proliferation/differentiation contraction
49
protein kinases
activate other proteins by transferring a phosphate group to them
50
second messenger model with cAMP and kinases
first messenger binds to receptor triggers the production of cAMP (cyclic adenosine monophosphate), which acts as a second messenger. cAMP activates Protein Kinase A (PKA). cascade where the signal is amplified: Each activated Protein Kinase A phosphorylates multiple downstream enzymes. Each enzyme activates more molecules (e.g., producing 100 end products). This exponential amplification allows a single signal to produce a large cellular response.
51
outcomes of kinase activation within a cell
ctive transport: Phosphorylation drives ion movement across the membrane. Microtubule function: Changes in transport, secretion, and cell shape. Enzyme activation: Enzyme 1 leads to lipid breakdown. Enzyme 2 leads to glycogen breakdown. Protein synthesis: Phosphorylation influences processes in the endoplasmic reticulum, such as calcium transport and protein production. Gene expression: Protein kinases can activate transcription (DNA → mRNA), leading to long-term cellular changes.
52
lipid soluble messengers
generally act by binding to intracellular receptor steroid hormones, thyroxine, sex hormones once inside the nucleus, a lipid soluble messenger would acts as a transcription factor slower response than with membrane receptors
53
water soluble messengers
binding to the extracellular portion of receptor proteins embedded in the plasma membrane (e.g. dopamine, adrenalin, melatonin)
54
critical points for water soluble messengers
broad range of receptors activate intracellular signalling cascades can activate downstream mediators faster response
55
Type A
receptors that are ligand-gated ion channels. Activation of the receptor by a first messenger (ligand) results in a conformational change to the receptor so it forms an open channel through the plasma membrane.
56
Type B
receptors that function as enzymes intrinsic enzyme activity and most are protein kinases that specifically phosphorylate the amino acid tyrosine (receptor tyrosine kinases)
57
Type C
Receptors that interact with cytoplasmic Janus Kinases (JAKs) dont have intrinsic kinase activity
58
Type D
G-Protein-Coupled receptors Bound to the inactive receptor is a protein complex located on the cytosolic surface of the plasma membrane and belonging to the family of heterotrimeric proteins known as G proteins.
59
type c mechanism
binding of ligand to receptor causes conformational change in receptor that leads to activation of cytoplasmic kinase
60
type b mechanism
Binding of messenger changes the conformation Receptor “autophosphorylates” its tyrosine groups Phosphotyrosines on the cytoplaasmic portion are docking sites for cytoplasmic proteins. Docking proteins bind and activate other proteins, which in turn activate other signaling pathways cytoplasmic proteins activated by phosphorylation
61
janus kinases
cytoplasmic kinase a family of 4 kinases that are all tyrosine kinases
62
3 subunits of G proteins
alpha: can bind Guanosine-diphosphate (GDP) “OFF” or Guanosine-triphosphate (GTP) “ON” beta gamma
63
type d mechanism
The binding of a ligand to the receptor changes the conformation of the receptor. This activated receptor increases the affinity of the alpha subunit for GTP. When bound to GTP, the alpha subunit dissociates from beta and gamma subunits. Activated alpha subunit links with another plasma membrane protein (effector protein, eg ion channels and enzymes)
64
signalling via adenyl cyclase and cyclic AMP:downstream signaling from G-Protein-Coupled receptors
The effector protein that is activated: the membrane enzyme adenylyl cyclase This catalyses the conversion of cytosolic ATP molecules to cyclic 3´,5´-adenosine monophosphate, or cyclic AMP (cAMP). Cyclic AMP then acts as a second messenger. Inside the cell, cAMP binds to and activates an enzyme known as cAMP dependent protein kinase. This is also called Protein Kinase A (PKA). PKA then phosphorylates downstream targets
65
Ca2+ in cells
maintained at very low concentration in cytosol so when first messenger binds to receptor and it opens, influx of Ca2+ into cytosol, also released from ER
66
Ca2+ as second messenger
binds to various cytosolic proteins, eg calmodulin. On binding with Ca2+ calmodulin changes shape, and this allows active calcium-calmodulin to activate or inhibit kinases such as calmodulin-dependent kinases which in turn can activate other proteins using ATP to phosphorylate them
67
cessation of receptor activation
decrease in concentration of first messenger molecules enzymes in vicinity metabolise the first messengers, or it is taken up by other cells or just diffuses away
68
how can receptors be inactivated
chemical alteration, phosphorylation, to lower affinity for first messenger plasma membrane receptors can be removed when the combination of first messenger and receptor is taken into the cell by endocytosis
69
Arachidonic acid
polyunsaturated fatty acid derived from phospholipids in the plasma membrane is a second messenger
70
arachidonic acid mechanism
first messenger binds to receptor phospholipase A2 causes arachidonic acid to split off from membrane can be metabolised by either cyclooxygenase pathway or lipoxygenase pathway
71
interfering with the cyclooxygenase pathway
aspirin inhibits it reduces inflammation and blood clotting
72
Corticosteroids
inhibit phospholipase A2 effects downstream signalling pathways
73
eicosanoids
prostaglandis cyclic endoperoxides thromboxanes leukotrines can act as intracellular messengers but are often released locally acting in a paracrine or autocrine manner to stimulate a variety of physiological responses

Human Physiology (12 decks)

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